1. Field of the Invention
This invention relates to an improved method for pneumatic threading in a two-for-one twister using a spindle of the double hollow mandrel type.
The invention relates particularly to a two-for-one twisting spindle in which the two yarn bobbins are each mounted on their own hollow mandrel with the yarns unwinding upwards, each yarn unwinding from its own bobbin to directly enter its own hollow mandrel without being conveyed, during its travel, into the space surrounding the other bobbin, all as described and claimed in European Pat.Appln.public. No. 0 417 850 in the name of the present applicant.
2 Description of the Related Art
The yarn braking device, which has long been known (two expansion half-capsules) is located in that portion of the central duct comprising the stationary part of the lower mandrel of the twisting spindle. Both yarns to be twisted together to form the twisted yarn pass through said lower hollow mandrel. Said yarns can be of any composition or structure, and will be known in the ensuing description and claims simply as yarns or twisted yarns, the terms being used interchangeably and including all filaments or filament assemblies or fibers, both natural and artificial. In two-for-one twisting, various types of spindles are known, and it is also known that threading the yarn through the central bore of the hollow mandrel is always a problem, as the operation is difficult and laborious. Numerous methods for simplifying this operation have been studied for the various types of twisting spindles. The present applicant has also filed various patent applications on this subject. In this respect, in the case of two-for-one twisters with a single central hollow mandrel automatic pneumatic threading is already well known, in contrast to spindles with a split central mandrel, in which replacing the empty bobbins with full bobbins, or re-starting the twisting process after an interruption for yarn breakage currently involves very costly and laborious operations of poor reliability. The applicant has therefore evolved and tried an improved method of extreme reliability for pneumatic threading in a spindle comprising a double central hollow mandrel for twisting together two yarns unwound from two overlying feed bobbins.
The improved method of the present invention has the following essential advantages:
it enables a two-for-one twisting spindle with a split central hollow mandrel to benefit from a method providing extremely reliable pneumatic threading each time the twisting process is to be restarted;
it allows rational automation of costly low-reliability operations, leading to a twisted yarn at lower operating cost;
it allows rapid and simple bobbin replacement.